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A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or patent disclosure as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyrights.
1. Field of the Invention
The present invention relates to pipelines that carry hydrocarbon products and other hazardous fluids, and more particularly, to an external three-dimensional secondary containment structure for pipeline transmission systems.
2. Description of Related Art
Pipeline transmission systems are in widespread use in the production, transportation, and distribution of oil, gas, water, hydrocarbon fluids such as petroleum products, and other hazardous fluids. Most pipeline transmission systems are constructed from welded single wall steel or aluminum pipe. Since at least the early 1950""s, single wall pipe sections have been externally and internally coated with various fusion bonded epoxy (xe2x80x9cFBExe2x80x9d) coatings to provide corrosion protection. While these early FBE formulations provided adequate corrosion resistance, they were known to suffer from a number of significant disadvantages. A significant disadvantage with FBE coatings relates to the procedures required to cure the coating. In particular, FBE coatings require baking at elevated temperatures to properly cure. In addition, FBE pipe coatings are expensive, and difficult and time consuming to apply due largely to curing requirements. In addition, once cured FBE coatings can be brittle and prone to chipping and cracking during handling and installation.
More recently, environmental concerns and legislative action have resulted in further efforts directed to reducing the potential for environmental contamination by improving the structural integrity and reliability of pipeline transmission systems. Since many pipelines carry liquids that are highly flammable, toxic, or corrosive, preventing leaks and the resulting environmental contamination is of paramount concern in the operation of pipeline transmission systems. As a result, various federal, state, and local governmental agencies, such as the United States Environmental Protection Agency (EPA), now require that pipelines conveying hazardous liquids or gases be adapted with secondary containment capabilities to prevent and/or reduce leak-related environmental contamination.
As a result of these concerns, risks, and potential liabilities, many owners and operators of pipeline transmission systems have experimented with the use of various secondary containment systems. One known method of providing secondary containment involves the installation of pipelines within a trench lined with an impermeable liner. Trench-type containment systems, however, are expensive to install, difficult to maintain, and are not suited for applications wherein a body of water must be traversed. Another common method for providing secondary containment involves the utilization of double-wall pipe, wherein radially spaced inner and outer pipe walls define an annular void for containing leaks. The use of double wall pipe, however, substantially increases material and installation costs. In addition, double wall pipe is less resistant to corrosion due to the bonding of metal to metal to form the pipe. Accordingly, the owners and operators of pipeline transmission systems are in need of an improved means for providing a secondary containment system that is reliable and cost effective.
The background art reveals several attempts to provide secondary containment systems and methods of leak detection suitable for use with pipelines. For example, U.S. Pat. No. 3,882,382, issued to Johnson, discloses a leak detecting conduit cover comprising ring-like sections sized for installation in surrounding relation with the pipe to be protected. The ring-like sections include an outer protective metallic cover plate, an insulating panel, and an electrically energized metal mesh that is electrically isolated from the other components. The components are configured such that moisture leaking from the conduit bridges a gap between the metal mesh and the outer metallic cover thereby completing a circuit and triggering an alarm or indicating signal. Another example is disclosed in U.S. Pat. No. 4,468,609, wherein there is disclosed a control system for detecting leaks in insulation-jacketed pipes. The system includes a heat-insulating jacket having radially open measuring chambers for receiving measuring probes, each of which has two electrodes arranged at sectional intervals and connected to an evaluation circuit. In addition, U.S. Pat. No. 4,821,915, issued to Mayer, discloses a double-wall pipe structure wherein a coupler assembly incorporates a leak-detecting sensor. U.S. Pat. No. 5,918,267, issued to Evans et al., discloses a system for detecting leaks from buried pipes that relies on a fabric fluid-wicking member that lies beneath the pipe and a fluid sensor in contact with the wicking member. Fluid leaking from the pipe is brought into contact with the sensor by the wicking member. These secondary containment systems are burdened with a number of disadvantages, reliability problems, cost issues, and complexities.
Secondary containment systems are also employed with aboveground and underground storage tanks. U.S. Pat. No. 4,523,454, issued to Sharp, discloses a storage tank system for storing liquid gasoline comprising a rigid inner tank encased by a flexible outer jacket with a leak detecting means associated with the space between the inner tank and jacket. Leak detection is achieved by detecting pressure fluctuations in the closed space. Positive pressurization is preferred, however, a vacuum may be used provided reinforcing members are incorporated to maintain the spaced relationship between the inner tank and outer jacket. U.S. Pat. No. 4,653,312, also issued to Sharp, discloses a method of fabricating a jacketed storage tank according to a method requiring the application of a separating agent over the storage tank, applying a layer of fibrous reinforcing material on the separating agent, and thereafter applying a resinous material. The separating agent insures that a subsequently applied fibrous reinforcing material will not adhere to the inner storage tank. U.S. Pat. No. 4,696,186, also issued to Sharp, discloses a storage tank system for storing liquid gasoline wherein a rigid inner tank is encased by a flexible outer jacket with a leak detecting means associated with the closed space therebetween. In this patent, Sharp discloses the use of gas pervious material to occupy the closed space between the tank and jacket.
U.S. Pat. No. 4,821,915, issued to Mayer, discloses a twin wall fiberglass tank having an inner wall, an outer wall, and a core disposed between the inner and outer walls which forms a plurality of air gaps. U.S. Pat. No. 4,871,078, issued to Sharp, discloses a method of making a jacketed storage tank comprises applying an open-cell synthetic foam over a rigid inner storage tank, applying a layer of fibrous reinforcing material on the separating agent, and applying a resinous material. U.S. Pat. No. 4,998,435, issued to Miller, discloses a method of testing pipe sections at an oil-rig floor by means of an internal pipe testing tool. U.S. Pat. No. 5,222,769, issued to Kaempen, discloses a double-wall composite pipe structure having separated impermeable inner and outer walls. U.S. Pat. No. 5,918,267, issued to Evans, discloses a system for detecting leaks from buried pipes that transport fluids other than water. U.S. Pat. No. 5,904,265, issued to Zanbergen et al., discloses a tank with inner and/or outer double-walled lining formed by a double walled cladding adhered to the outer surface and consisting of a double pile fabric which is reinforced by a curable impregnated resin, such that the upper and lower fabric are connected in spaced relation by means of webs formed by pile threads.
The secondary containment systems and methods disclosed in the background art have not gained widespread acceptance largely due to the complexity of installation, reliability and cost. Another significant disadvantage with secondary containment systems of the background art is a lack of impact resistance. Accordingly, there exists a need for an improved secondary containment system for use primarily with aboveground and/or underground pipelines.
The present invention provides a system and method for providing secondary containment and leak detection for pipeline transmission systems. The system and methods disclosed herein provide a secondary containment system for pipelines which complies with environmental regulations for double wall applications. The present invention provides a secondary containment system for pipeline transmission systems wherein the external surface is supplemented with an resin bonded multi-ply fabric which forms a secondary containment structure external to the pipe with first and second spaced layers forming an interstitial space therebetween. An external coating of cured resin, such as epoxy resin, provides resistance to impact, abrasion, and chemically induced corrosion and deterioration. Probes may be installed at various locations along the pipeline for continuously sampling the environment within the interstitial space thereby providing leak detection.
Secondary containment is constructed on an existing section of, steel, iron, or concrete pipe in accordance with the following procedures. The outer surface of the pipe provides a substrate for application of the secondary containment system. As applied to steel pipe, the instant method generally includes the following steps: (1) preliminary surface preparation to provide a suitable substrate for application of the secondary containment system; (2) application of an optional primer coat (depending on the pipe material); (3) initial lay-out, measuring, and cutting of multi-ply fabric comprising an upper fabric and a lower fabric which are held together by connecting pile threads; (4) application of a liquid epoxy resin to the outer surface of the pipe; (5) application of multi-ply fabric sections into the wet epoxy film using roller to remove entrapped air; (6) application of an additional coating of epoxy resin to ensure complete saturation; (7) curing of the cloth/epoxy composite, which results in the separation of the upper and lower fabric to form an interstitial space therebetween; (8) application of a layer of impact and chemically resistant curable resin to form an outer shell; and (9) installation of an optional monitoring system capable of interstitial monitoring at approximately 1000 ft. sampling intervals.
Accordingly, it is an object of the present invention to provide a secondary containment system for aboveground and underground pipelines.
Still another object of the present invention is to provide a method for installing a secondary containment system on pipelines that provides an interstitial space suitable for use in leak detection.
Yet another object of the present invention is to provide a secondary containment system for pipelines that results in multiple corrosion resistant outer layers to protect the enclosed pipeline from corrosion induced failure.
In accordance with these and other objects that will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings.